The present invention relates to a process for producing a modified polymer rubber having superior impact resilience. The modified polymer rubber obtained according to said process is most suitable for motorcar tires having superior fuel cost saving.
A styrene-butadiene copolymer obtained by emulsion polymerization is known as rubber used for motorcar tires. However, said copolymer has a problem that motorcar tires comprising said copolymer are not satisfactory from a viewpoint of fuel cost saving, because the copolymer does not have sufficient impact resilience.
In order to obtain rubber having superior impact resilience, JP-A60-72907 discloses a process, which comprises copolymerizing butadiene and styrene in a hydrocarbon solvent using an organolithium compound as an initiator, and a Lewis base such as ether as a microstructure controlling agent.
Further, Japanese Patent No. 2540901 proposes a process, which comprises reacting an alkali metal, which is bound at the end of a diene polymer rubber, with a specific acrylamide to obtain a modified diene polymer rubber having improved impact resilience.
Furthermore, Japanese Patent Application No. 2000-328813 discloses a process, which comprises reacting an alkali metal, which is bound at the end of a diene polymer rubber, with a specific amine to obtain a modified diene polymer rubber having improved impact resilience and processability.
However, recently, a level of a demand for fuel cost saving of motorcar tires is higher from an environmental view, and therefore, any of the above-mentioned copolymer rubbers can hardly meet such a demand.
An object of the present invention is to provide a process for producing a modified polymer rubber having superior impact resilience.
The present invention provides a process (the process being hereinafter referred to as xe2x80x9cProcess-1xe2x80x9d) for producing a process for producing a modified polymer rubber having modified both ends, which comprises the steps of:
(1) reacting a compound represented by the following formula (1) with an organic alkali metal compound, to produce a chemical species, 
wherein R1 is an amino, alkoxy, silyloxy, acetal; carboxyl or mercapto group or a group derived from any of these groups,
(2) polymerizing a conjugated diene monomer or a combination of a conjugated diene monomer with an aromatic vinyl monomer in the presence of the chemical species to produce an active polymer having an alkali metal at an end thereof, and
(3) reacting the active polymer with a functional group-carrying modifying agent in a hydrocarbon solvent to produce the modified polymer rubber having modified both ends.
The present invention also provides a process (the process being hereinafter referred to as xe2x80x9cProcess-2xe2x80x9d) for producing a modified polymer rubber having modified both ends, which comprises the steps of:
(1) reacting a compound represented by the above formula (1) with an organic alkali metal compound to produce a chemical species,
(2) polymerizing a conjugated diene monomer or a combination of a conjugated diene monomer with an aromatic vinyl monomer in the presence of the chemical species to produce an active polymer having an alkali metal at an end thereof,
(3) reacting the active polymer with a compound represented by the above formula (1) to produce an active polymer, each of whose both terminals is modified and has an alkali metal, and
(4) reacting the active polymer with a functional group-carrying modifying agent in a hydrocarbon solvent to produce the modified polymer rubber having modified both ends.
Examples of a conjugated diene compound used in the present invention are 1,3-butadiene, isoprene, 1,3-pentadiene (piperylene), 2,3-dimethyl-1,3-butadiene and 1,3-hexadiene. Of these, 1,3-butadiene and isoprene are preferable from a viewpoint of availability and physical properties of a modified polymer rubber obtained.
Examples of an aromatic vinyl compound used in the present invention are styrene, xcex1-methylstyrene, vinyltoluene, vinylnaphthalene, divinylbenzene, trivinylbenzene and divinylnaphthalene. Of these, styrene is preferable from a viewpoint of availability and physical properties of a modified polymer rubber obtained.
In the above formula (1), a preferable R, is an N,N-dimethylamino group, an N,N-diethylamino group, an N,N-dipropylamino group, an N,N-dibutylamino group or a morpholino group.
Examples of the compound represented by the formula (1) are 1-(4-N,N-dimethylaminophenyl)-1-phenylethylene, 1-(4-N,N-diethylaminophenyl)-1-phenylethylene, 1-(4-N,N-dipropylaminophenyl)-1-phenylethylene, 1-(4-N,N-dibutylaminophenyl)-1-phenylethylene and 1-(4-morpholinophenyl)-1-phenylethylene. Particularly, 1-(4-N,N-dimethylaminophenyl)-1-phenylethylene and 1-(4-morpholinophenyl)-1-phenylethylene are preferable from a viewpoint of remarkable improvement of fuel cost saving.
Although a compound having two polar groups can be also used as the compound represented by the formula (1) to attain the objects of the present invention, a compound having one polar group is industrially preferable from a viewpoint of solubility of said compound into a hydrocarbon solvent.
Examples of the organic alkali metal compound used in the present invention are hydrocarbon compounds containing a metal such as lithium, sodium, potassium, rubidium and cesium. Among them, preferable are lithium compounds or sodium compounds having 2 to 20 carbon atoms.
Specific examples thereof are ethyllithium, n-propyllithium, iso-propyllithium, n-butyllithium, sec-butyllithium, t-octyllithium, n-decyllithium, phenyllithium, 2-naphthyllithium, 2-butyl-phenyllithium, 4-phenyl-butyllithium, cyclohexyllithium, 4-cyclopentyllithium and 1,4-dilithio-butene-2. Among them, n-butyllithium or sec-butyllithium is preferable to obtain an active polymer having a narrow molecular weight distribution at a rapid reaction rate.
When a combination of a conjugated diene monomer with an aromatic vinyl monomer is used in the step (2) in the present invention, a weight ratio of conjugated diene compound/aromatic vinyl monomer is preferably from 50/50 to 90/10, and more preferably from 55/45 to 85/15. When the ratio is less than 50/50, the active polymer obtained may be insoluble in the hydrocarbon solvent, and as a result, it may be impossible to carry out a homogeneous polymerization. When the ratio exceeds 90/10, strength of the active polymer obtained may decrease.
A polymerization method in the step (2) is not particularly limited, and maybe a conventional one. In said step, it is permitted to use conventional solvents and additives usually used in the art such as hydrocarbon solvents; randomizers; and additives used for controlling a content of a vinyl bond (which bond is derived from the conjugated diene monomer) in the active polymer obtained.
As the above-mentioned additives used for controlling a content of a vinyl bond, Lewis basic compounds are exemplified. As said compounds, an ether or a tertiary amine is preferable from a viewpoint of industrial availability.
Examples of the above-mentioned ethers are cyclic ethers such as tetrahydrofuran, tetrahydropyran and 1,4-dioxane; aliphatic mono ethers such as diethyl ether and dibutyl ether; aliphatic diethers such as ethylene glycol dimethyl ether, ethylene glycol diethyl ether, ethylene glycol dibutyl ether, diethylene glycol diethyl ether and diethylene glycol dibutyl ether; and aromatic ethers such as diphenyl ether and anisole,
Examples of the above-mentioned tertiary amines are triethylamine, tripropylamine, tributylanine, N,N,Nxe2x80x2,Nxe2x80x2-tetramethylethylenediamine, N,N-diethylaniline, pyridine and quinoline.
Examples of the functional group-carrying modifying agent (hereinafter simply referred to as xe2x80x9cmodifierxe2x80x9d) used in the present invention are cyclic ether structure-carrying compounds such as ethylene oxide, propylene oxide, glycidyl methaorylate, tetraglycidyl-m-xylenediamine, tetraglycidyl-1,3-bisaminomethylcyclohexane, tetraglycidyldiaminodiphenylmethane, tetraglycidyl-p-phenylenediamine, diglycidylaniline and diglycidyl-o-toluidine; ketone compounds such as 4-dimethylaminobenzophenone, 4-diethylaminobenzophenone, 4-morpholinobenzophenone and 4-morpholinoacetophenone; acrylamide compounds such as dimethylacrylamide, diethylacrylamide and dimethylaminopropylacylamide; cyclic amine compounds; and linear amine compounds. Of these, cyclic amine compounds and linear amine compounds are particularly preferable, from a viewpoint such that (1) solubility thereof to a solvent is superior, and (2) fuel cost saving can be remarkably improved.
Examples of the above-mentioned cyclic amine compounds are
1,3-dimethyl-2-imidazolidinone,
1,3-diethyl-2-imidazolidinone,
1,3-dipropyl-2-imidazolidinone,
1-methyl-3-ethyl-2-imidazolidinone,
1-methyl-3-propyl-2-imidazolidinone,
1-methyl-3-butyl-2-imidazolidinone,
1-methyl-3-(2-ethoxyethyl)-2-imidazolidinone and
1,3-dimethyl-3,4,5,6-tetrahydropyrimidinone.
Specific examples of the above-mentioned linear amine compounds are 1,1-dimethoxytrimethylamine, 1,1-diethoxytrimethylamine, 1,1-di-n-propoxytrimethylamine, 1,1-di-iso-propoxytrimethylamine, 1,1-di-n-butoxytrimethylamine and 1,1-di-tert-butoxytrimethylamine.
Among the above-mentioned cyclic amine compounds and linear amine compounds, a low molecular weight amine such as 1,1-dimethoxytrimethylamine or 1,3-dimethyl-2-imidazolidinone is preferable from a viewpoint that fuel cost saving can be remarkably improved by using a small amount thereof.
A hydrocarbon solvent used in Process-1 or Process-2 in accordance with the present invention comprises those solvents, which do not deactivate the organic alkali metal compound. Preferable examples thereof are aliphatic hydrocarbons, aromatic hydrocarbons and alicyclic hydrocarbons. Particularly preferable examples thereof are those having 2 to 12 carbon atoms. Specific examples thereof are propane, n-butane, iso-butane, n-pentane, iso-pentane, n-hexane, cyclohexane, propene, 1-butene, iso-butene, trans-2-butene, cis-2-butene, 1-pentene, 2-pentene, 1-hexene, 2-hexene, benzene, toluene, xylene and ethylbenzene, and a combination of at least two thereof.
An amount used of the modifier is usually from 0.1 to 10 mol, and preferably from 0.5 to 2 mol, per 1 mol of the active polymer. When the amount is less than 0.1 mol, an improving effect of fuel cost saving may be small. When the amount exceeds 10 mol, the unreacted modifier remains in the solvent. It is not recommendable from an economical point of view, because an additional step of separating the modifier from the solvent is required in order to recycle and reuse the solvent.
The reaction of the step (3) in Process-1 and the reactions of the steps (3) and (4) in Process-2 proceed rapidly. As a preferable contacting method, there are exemplified (1) regarding Process-1, a method comprising the step of adding the modifier to the reaction mixture obtained in the step (2), and (2) regarding Process-2, a method comprising the steps of (i) adding the compound represented by the formula (1) to the reaction mixture obtained in the step (2), and (ii) adding the modifier to the obtained reaction mixture. A reaction temperature is generally from ambient temperature to 80xc2x0 C., and a reaction time is generally from several seconds to several hours.
From a viewpoint of kneading processability of the modified polymer rubber obtained, it is permitted to add a coupling agent represented by the following formula to the active polymer, (1) prior to or after the step (3) regarding Process-1, and (2) prior to or after the step (3) or prior to or after the step (4) regarding Process-2,
RaMX4-a 
wherein R is an alkyl, alkenyl, cycloalkenyl or aromatic hydrocarbon group; M is a silicon or tin atom; X is a halogen atom; and a is an integer of from 0 to 2.
An amount added of the above-mentioned coupling agent is usually from 0.03 to 0.4 mol, and preferably from 0.05 to 0.3 mol, per 1 mol of the active polymer. When the amount is less than 0.03 mol, an improving effect of processability of the modified polymer rubber may be small. When the amount exceeds 0.4 mol, a proportion of the active polymer participating in the reaction with the modifier decrease, so that an improving effect of fuel cost saving may decrease.
The modified polymer rubber contained in the reaction mixture obtained in the step (3) of Process-1 or in the step (4) of Process-2 can be solidified according to a solidifying method, which is usually carried out in the production of rubber by solution polymerization, such as (1) a method comprising the step of adding a coagulant and (2) a method comprising the step of adding steam. A solidifying temperature is not particularly limited.
The solidified modified polymer rubber separated can be dried with a drier such as a band drier and an extrusion type drier, which are commonly employed in a synthetic rubber production. A drying temperature is not limited.
Mooney viscosity (ML1+4) of the obtained modified polymer rubber is preferably from 10 to 200, and more preferably from 20 to 150. When the Mooney viscosity is less than 10, mechanical properties such as tensile strength of vulcanized rubber thereof may decrease. When the Mooney viscosity exceeds 200, miscibility when blending said modified polymer rubber with the other rubber to produce a rubber composition may be so poor that it is difficult to produce said rubber composition, and as a result, mechanical properties of a vulcanized rubber composition thereof may decrease.
A content of the vinyl bond (which bond is derived from the conjugated diene monomer) contained in the obtained modified polymer rubber is preferably from 10 to 70%, and more preferably from 15 to 60%. When the content is less than 10%, a glass transition temperature of the modified polymer rubber obtained may be lowered to deteriorate a grip performance of motorcar tires composed of the modified polymer rubber. When the content exceeds 70%, a glass transition temperature of the modified polymer rubber obtained may be elevated to deteriorate the impact resilience of the modified polymer rubber.
The obtained modified polymer rubber can be used in combination with other components such as other rubbers and various additives.
Examples of the other rubber are styrene-butadiene copolymer rubber obtained by emulsion polymerization; polybutadiene rubber, butadiene-isoprene copolymer rubber and styrene-butadiene copolymer rubber obtained by solution polymerization using catalysts such as an anion polymerization catalyst and a ziegler type catalyst; natural rubber; and a combination of at least two thereof.
As to the rubber composition comprising the other rubber and the modified polymer rubber, a proportion of the latter rubber is preferably not less than 10% by weight, and more preferably not less than 20% by weight, based on 100% by weight of a total weight of both rubbers. When the proportion is less than 10% by weight, the impact resilience of the rubber composition obtained may hardly be improved, and also processability thereof is not good.
A kind and an amount of the above-mentioned additives can by determined depending upon purposes of using the rubber composition obtained. Examples of the additives usually employed in a rubber industry are vulcanizing agents such as sulfur; stearic acid; zinc white; thiazol type vulcanization accelerators; vulcanization accelerators such as thiuram type vulcaniztion accelerators and sulfenamide type vulcanization accelerators; organic peroxides; reinforcing agents such as carbon black of HAF and ISAF grades; fillers such as silica, calcium carbonate and talc; extender oils; processing coagents; and antioxidants.
A process for producing the above-mentioned rubber composition is not limited. An example thereof is a process comprising the step of mixing respective components with use of a known mixer such as a roll and a Bambury mixer. The resulting rubber composition is usually vulcanized, and is used as a vulcanized rubber composition.
Since the modified polymer rubber obtained by the process in accordance with the present invention is superior in impact resilience and processability, a rubber composition comprising said rubber is most suitable for motorcar tires having superior fuel cost saving. Said rubber composition can be also employed fuel uses such as the sole of a shoe, floor materials and rubber vibration insulators.